Osteoarthritis (OA) is a major cause of disability in the general population and is increased in Veterans. There are currently no effective pharmacologic agents capable of preventing or altering the course of disease. This project will use a novel interventional nanomedicine approach for preventing OA. Specifically, we will use targeted inhibitors to block activation of nuclear factor kappa B (NF?B) and expression of the downstream signaling elements that result in expression of matrix metalloproteinase-13 (MMP-13), a collagenase responsible for degradation of type II collagen in articular cartilage. Our hypothesis is that interruption of the signaling pathway initiated by NF?B and propagated by hypoxia inducible factor-2 alpha (HIF-2?) will prove extremely effective in early OA. By reducing MMP-13 we will prevent the irreversible loss of type II collagen responsible for much of the pathology. To test our hypothesis, we will use a mouse model of OA induced by destabilization of the medial meniscus (DMM). To prevent disease we will use a cell-permeable peptide (NBD) that has proven effective in experimental inflammatory arthritis. The severity and progression of OA induced by DMM in the treated mice will be quantitated by in vivo imaging using diagnostic near-infrared fluorescent (NIF) monoclonal antibody to type II collagen (MabCII) and confirmed by histopathology of the joints. Efficacy of the NBD peptide to inhibit NF?B activation in vivo will b evaluated in mice with a transgene containing NF?B responsive elements in the promoter upstream from a luciferase reporter. Hypoxia-inducible factor (HIF- 2?, encoded by EPAS1) has been shown to be responsible for expression of MMP-13 and OA in the DMM model. We will examine the hypothesis that NF?B activation is a critical early point for induction of OA in joint instability and that prevention of its activation will block the downstream induction of expression of HIF-2? and ultimately expression of its target genes such as matrix metalloproteinase MMP-13. Microarray analyses on RNA from the DMM mouse knee will be used to discover genes that are linked to NF?B activation. To establish the feasibility and efficacy of using a targeted delivery system to suppress arthritis we will employ antibody- targeted nanosome encapsulation to deliver the therapeutic agent to specific local sites. Nanosomes will be targeted using a monoclonal antibody to type II collagen (MabCII) for localization to damaged cartilage or antibody to Lyc6 for localization to activated macrophages. Synthetic inhibitors of MMPs have proven problematic in clinical trials due to musculoskeletal pain, fibrosis and tendonitis. We will overcome that problem by selectively blocking only locally produced MMP-13 with an inhibitor packaged within a pH-responsive, endosomolytic smart polymer nanoparticle (SPN). The nanoparticle is unique in that it localizes to specific sites but remains packaged until it is released by MMP-13 proteolytic activity (proximity activated targeting; PAT) due to the incorporation of an MMP-13 peptide in the outer shell. Methods for fully evaluating the development of disease and expression of the mediators involved are proposed. These experiments provide a novel approach to managing what has heretofore been an intractable problem.